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Old 08-06-2013, 02:58 PM   #1
2 Rivet Member
1973 29' Ambassador
Seattle , Washington
Join Date: Aug 2012
Posts: 90
Question Add Gray Tank to 70's Rear Bath


I've searched and read just about every thread on adding gray tanks on AF, but didn't see if anyone has done what I'm hoping to accomplish.

I have a 1973 Rear Bath (mid twin bed) 29' Ambassador.

This has a 17 Gallon black tank, but no gray water tank (I have to use an external tote for gray water and it's inconvenient and unsightly).

Since I have a 45 Gallon fresh tank, I'd like to add 25-30 gallons of gray water capacity.

What do I know:
I know that Andy has done some conversion in his shop, but my local shop says it's not possible to do (which probably means they don't want to mess with it)

I know several folks here have done them as part of a MAJOR restoration, but my trailer is in fine shape, so I want to do this with as little deconstruction as absolutely possible.

I also know that the following year (74), the factory started including a small gray tank as standard, so there MUST be an easy way to move a little plumbing around and locate a similar size tank to what they used.


Can anyone help point me to a solution? Ideally, I could find someone up here (seattle, WA) that would just do the whole job for me, but failing that, specifics from someone in a similar situation would be helpful.


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Old 08-06-2013, 03:37 PM   #2
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1981 31' Excella II
New Market , Alabama
Join Date: Sep 2011
Posts: 5,280
I expect you can fit the tank between frame members or even above the floor if you had some sort of sump pump for the shower drain. You want to make sure you put the tank forward so as no to overstress the already overstressed rear frame.


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Old 08-06-2013, 03:55 PM   #3
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1973 29' Ambassador
Seattle , Washington
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Posts: 90
Thanks Perry, I can look into this, but am hoping someone has done this so I don't have to drop the whole belly to do this thing. Or perhaps I can ferry down to CA or AL and get Inland or OODM to do it up
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Old 08-06-2013, 04:01 PM   #4
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1997 34' Limited
1970 27' Overlander
South of Atlanta , Georgia
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I am currently tearing apart my 1970. It appears that some PO either added a grey tank, or plumbed the shower and sink drains into the black tank. I will know for sure when I pull the body off of the frame in the next couple of weeks. Through the rot in the rear floor I can see a tank that the grey goes into and it is very close to where the toilet sat. At present I can't be positive if they are the same tank.
Craig and Carol
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Old 08-06-2013, 07:29 PM   #5
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1974 Argosy 26
Morrill , Nebraska
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My '74 Argosy 26' has the original 12 gallon grey water tank. It is located about 30" forward of the rear bumper.
I too did not like having to carry and use a tote. I have a 10 gallon tote and used it for 3 years. At only 10 gallons it would not hold the entire contents of the full grey water tank. Plus dragging the 80+ pound tote (when full) to the dump station was a hassle.
Not wanting to tear the floor or belly pan off to install a larger tank.
I took a different approach. Since the coach has twin beds. And the drain for the galley sink runs under the curb side bed.
I installed a 21 gallon tank under the curb side bed. Connected the new tank drain line to the existing galley drain line. There is a ball valve in the new tank drain line. Which gives me control of when the tank is to be emptied.
I installed a 12 volt pump in the trunk and piped the discharge of the pump to the new tank. Also piped in a vent to the new tank using 1/2" PVC and a flexible stainless steel hose.
The inlet of the GW pump is connected to an inline filter. From the inlet side of the filter is a 6' washer hose, which has female hose fittings on each end.
I have a Valtera end cap with a garden hose fitting to which I connect the washer hose.
When the original grey water tank is full. I pump the contents into the new tank. By opening the dump valve for the original GW tank, it floods the inlet to the grey water pump. I start the pump and run it until the original tank is empty. Takes about 4 minutes.
I now have 33 gallons of grey water capacity.
When both tanks are full. A trip to the dump station is in order.
When I get to the dump station. I open the original GW dump valve as I always have. Then go inside and open the dump valve (ball valve) for the new GW tank. It discharges into the original GW tank, thru the tank and out to the sewer.
We just completed a 4,000 mile trip to Canada. While this setup is unorthodox, it worked without a problem.
The new tank reduced the under bed storage capacity by 2 compartments. By adding more storage space in the galley and dinette area. The results are a net plus for GW capacity as well as storage capacity.
I have a friend who used my idea and install a GW tank in his pre 74 trailer. No GW tank in his coach originally. While the setup is different from mine. Meaning he pumps the GW into the tank, then by switching some valves, uses the same pump to empty the tank. It still beats dealing with a tote.
These systems show there are alternatives to tearing into the coach belly pan or floor to add grey water capacity.
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Old 08-07-2013, 08:21 AM   #6
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1973 21' Globetrotter
Houston , Texas
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Vintage Trailer Supply sells a custom 16 gallon tank that will fit nicely in your belllypan and not hang down. I installed two of these in my '73 GT, one in each of the two bays immediately behind the axle. Yes, this was part of a complete renovation, but people add grey tanks to vintage trailers all the time without redoing the entire thing. It does take some planning to accomplish--you need to know where you are going to vent the tanks, and how they will fill and drain.

You will need to drop your bellypan pretty much from the axle on back. You will spend a fair amount of time on your back if you do the installation your self. The existing grey water plumbing will need to be reconfigured, but that is just part of the job, not a major deconstruction. There really isn't anything else in these bays behind the axle besides funky insulation and mouse nests, so you needn't worry about having to do too much rework.

good luck!
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Old 08-07-2013, 11:13 AM   #7
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1973 29' Ambassador
Seattle , Washington
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Posts: 90
Wow! Thanks to everyone for the help. I will have to consider Belegedhel and TG's ideas and see what might work best. I can see the pros and cons of both, so will have to think about this.

Any other ideas/approaches that I might not have considered?

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Old 08-23-2013, 11:22 AM   #8
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1973 29' Ambassador
Seattle , Washington
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Update, my local dealer doesn't do it, but the dealer about 4 hours away will do it for "around $1K" parts and labor, so it looks like a long day road trip is coming up for me!
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Old 08-23-2013, 11:45 AM   #9
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Bothell , Washington
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I recall the author from "Restoring a Dream" adding a grey water tank to his older Overlander (I believe) - a 60's model. First he had a custom tank fabricated (two actually, he made a new black water tank).

He managed to snug the new grey water tank down into the frame a bit, and it was a very flat tank design. I don't recall the specific details, but it did require going into an adjoining closet in the kitchen area - which had the hidden benefit of putting it closer to the kitchen lines.

It'll be tricky if your shower is on the opposite side as your kitchen sink, but as long as you can get the shower pan above the tank, enough for it to drain into it, you should be fine.

I see you're in Seattle - drop me a line if you'd like a name of a shop that might be willing to do this for you as well.
Christopher Doll
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Old 08-23-2013, 01:05 PM   #10
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1973 25' Tradewind
Beautiful , Oregon
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Look up Top's "Abby gets all the attention" for some great pictures and installation ideas. He used Ronco Tanks I followed his lead and think I got the job done well. We shall see upon use

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Old 08-23-2013, 03:28 PM   #11
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1967 22' Safari
Long Beach , California
Join Date: Nov 2004
Posts: 85
Hello dcheshire:

Airstream Certified Service Center ( in Bellflower, CA - Toll Free (800) 662-3790 installed a grey water tank for me about four years ago. he charged me about half of the price of your quote. I'll bet he would give you a firm quote over the telephone.
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Old 08-23-2013, 06:10 PM   #12
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1973 29' Ambassador
Seattle , Washington
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Thanks everyone. Helmsman, i'll look them up. Blackbird, just sent you a PM.

thanks all!
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Old 08-23-2013, 06:56 PM   #13
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1976 Argosy 24
now being enjoyed by Heath and Mary in , Vermont
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If you open this older thread you'll find a lot of information, including photographs, about what you want to do.

Open and read the internal link at post # 36 as well.

Good luck,


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Old 08-23-2013, 08:13 PM   #14
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1968 24' Tradewind
1959 17' Pacer
Vintage Kin Owner
holly springs , Georgia
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Posts: 404
My 68 tradewind has a grey water tank installed just aft of the rear wheels below the belly pan. A hose connects this tank to the rear thetford valve cap.The tank has its own thetford dump valve when full. It was installed before I got it but looks like an easy project.

I was worried about clearance but in reality the bumper will drag before the tank does.

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